The SNF2, SNF5, and SNF6 genes of the yeast S. cerevisiae are required for transcription of a broad range of genes that are regulated by different mechanisms. Genetic studies of SNF proteins fused to the LexA DNA-binding domain showed that the SNF2, SNF5, and SNF6 (SNF2,5,6) proteins function interdependently in transcriptional activation, probably forming a heteromeric complex. Here, we propose studies to elucidate the roles of the SNF2,5,6 proteins in transcriptional activation. Further genetic analysis of activation by the LexA-SNF2,5,6 proteins will examine the relationships of SNF2,5,6 to one another and to other proteins that may be functionally related, including SPT4,5,6 SSN6 and GAL11. Biochemical methods will be used to confirm the physical association of the SNF2,5,6 proteins in a complex. Preliminary data suggest that SNF2,5,6 affect transcription of a wide variety of genes by acting coordinately with various gene-specific transcriptional activators. To test this idea, we will examine the effects of snf mutations on activation by LexA fusions to GAL4, Bicoid, GCN4 and RAP1. To identify functional domains of the SNF2,5,6 proteins, we will construct new LexA fusion proteins containing partial SNF sequences; the significance of unusual sequence features and regions of homology to other proteins will be examined. Recently, we identified an essential gene, STH1, with 60-80% identity to SNF2 over ~1000 codons. We propose studies to determine whether the STH1 protein has a role in transcriptional activation. Finally, both genetic and biochemical approaches will be used to identify genes encoding proteins that interact physically with SNF2,5,6. These interacting proteins may include additional proteins that contribute to transcriptional activation by SNF2,5,6. Most important, these studies should also identify the protein(s) of the transcriptional apparatus that are the targets for activation by SNF2,5,6. The proposed studies will contribute to our understanding of the mechanism of transcriptional activation in eukaryotic cells. Many oncoproteins are transcription factors, and aberrant transcriptional activation results in cellular transformation and cancer.